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// 440. K-th Smallest in Lexicographical Order
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
// given two integers 'n' and 'k', return the k'th lexicographically smallest
// integer
int count_prefix(int n, long long prefix) {
long long offset = 10, target = n;
int total = 0;
for (int i = 1; i <= 9; i++) {
long long min = prefix * offset;
long long max = min + offset - 1;
if (target < min)
break;
total += fmin(target, max) - min + 1;
}
return total + 1;
}
int findKthNumber(int n, int k) {
int prefix = 0;
if (k)
for (int i = !prefix ? 1 : 0; i <= 9; i++) {
int prefix_cnt = count_prefix(n, 10 * prefix + i);
if (k <= prefix_cnt)
return findKthNumber(n, k - 1);
k -= prefix_cnt;
}
return prefix;
}
int main() {
printf("%d\n", findKthNumber(13, 2)); // expect: 10
printf("%d\n", findKthNumber(1, 1)); // expect: 1
}
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